Make yarn interactive commands run in Git Bash/MSYS environment

[thetrompf]

The problem is caused by mintty, and it manifests weirdly because in most circumstances you can get interactive node programs to work because of a hack introduced via aliasing/wrapping commands in the bash profile:

bkc@DESKTOP-NNSLT74 ~/workspace/yarn-test $ type node
node is aliased to `winpty node.exe'

After a bit of digging I found the culprit in /etc/profile.d/aliases.sh

case "$TERM" in
xterm*)
        # The following programs are known to require a Win32 Console
        # for interactive usage, therefore let's launch them through winpty
        # when run inside `mintty`.
        for name in node ipython php php5 psql python2.7
        do
                case "$(type -p "$name".exe 2>/dev/null)" in
                ''|/usr/bin/*) continue;;
                esac
                alias $name="winpty $name.exe"
        done
        ;;
esac

Git bash wraps node, ipython, php, php5, psql, python2.7 in a program called winpty
which means when yarn invokes node, this hack is not invoked as well.

Related to issue #743

Test plan

I'm not sure how to setup an environment that could run an automated test for this case correctly
but I made the following before and after test:

bkc@DESKTOP-NNSLT74 ~/workspace/yarn-test $ ./bin/yarn init
yarn init v0.17.10
error An unexpected error occurred: "Can't answer a question unless a user TTY".
info If you think this is a bug, please open a bug report with the information p                                                                                                                                                    rovided in "C:\\Users\\bkc\\workspace\\yarn-test\\yarn-error.log".
info Visit https://yarnpkg.com/en/docs/cli/init for documentation about this com                                                                                                                                                    mand.

After wrapping the process in winpty:

bkc@DESKTOP-NNSLT74 ~/workspace/yarn-test $ ./bin/yarn init
yarn init v0.17.10
question name (yarn-test):

[Daniel15]

Awesome, thank you!